Two stage welder and method of operating same

ABSTRACT

An electric arc GMAW welder is provided, which welder includes a high speed switching power supply with a controller for creating a first or second weld process across the gap between a workpiece and a welding wire advanced toward the workpiece. The first process uses a first current waveform and the second process uses a second current waveform. A circuit is provided for shifting between the first and second weld processes. The shifting circuit includes a counter for counting the waveforms in the first and second processes and a circuit to shift from the process being processed to the other weld process when the waveform count of the weld process being processed reaches a preselected number for such weld process.

This application is a continuation-in-part of pending application Ser.No. 866,358 filed May 29, 2001 and owned by Assignee of thisapplication.

The invention relates to the art of electric arc welding and moreparticularly to an electric arc welder having two stage or two modeoperation and the method performed by this two stage electric arcwelder.

INCORPORATION BY REFERENCE

As background information, prior pending application Ser. No. 866,358filed on May 29, 2001 together with references incorporated by referencein that application are hereby incorporated by reference. Kawai U.S.Pat. No. 4,889,969 shows a switch to shift between DIP welding and pulsewelding and is incorporated by reference as background technology.

BACKGROUND OF INVENTION

Electric arc welders of the GMAW type are often powered by a high speedswitching power supply or power source with a controller for controllingthe current waveform of the welding process. The Lincoln ElectricCompany of Cleveland, Ohio has pioneered the concept of an electric arcwelder with a wave shaper to control the shape of the current waveformduring each cycle by the use of high frequency current pulses, themagnitude of each pulse being controlled by a pulse width modulator. Insuch welders, the wave shape of the current is accurately controlled toperform such diverse welding processes as pulse welding, constantvoltage welding, spray welding, pulse welding, short-arc CV welding andSTT welding. In such processes, the wave shape for each weld cycle iscontrolled by the pulse width modulator to produce a series of weldingcycles that perform a designated process. Such arc welders are quiteversatile; however, they are operated in selected mode by controllingthe pulses created by the waveform shaper.

THE INVENTION

The present invention relates to an electric arc welder, of the typementioned above, where the controller is shifted between two separateand distinct welding processes or welding modes. In accordance with theinvention, the pulse shaper or pulse generator shapes a series of pulsesforming a first welding process. The controller is shiftable to thenperform a second welding process by implementing a series of differentpulse shapes constituting a different mode of operation. By counting thecycles in the first mode of operation, the first process is terminatedand the second process is initiated. Thereafter, the cycles of the nextprocess are counted until they reach a set number, which indicates thatthe welder is to be shifted back to the first welding process. Thus, theelectric arc welder has the capability of performing two separatewelding processes by switching the controller from one mode of operationto another mode of operation. By this unique two stage or two stateoperation of an electric arc welder, the welder can perform a weldingoperation alternately using a first process and then a second process.For instance, a high energy process is performed for a short time andthen the welder is converted to a low energy weld process. If the twoprocesses are STT, low energy STT cycles are implemented followed byimplementation of high energy STT cycles. Thus, in one embodiment, thefirst process is a high energy process and the second is a low energyprocess. A counted number of cycles of each process are used in thewelding process to perform a total welding operation by implementing inseries the first and second welding processes. As an example, in onespecific embodiment the first process is a constant voltage sprayprocess with high heat. The second process is a pulsed GMAW or low heatwelding process. In the welding operation, the controller firstimplements the first process for a number of cycles and then the secondprocess for a number of cycles. In another embodiment of the invention,the first process is a pulse welding process where the pulses have highenergy or high heat. This is used in sequence with a low heat STT weldprocess for a number of cycles. By alternating between the pulse cyclesand the STT cycles, a desired total welding operation is performed. Inanother embodiment, the first process is a pulse welding process havinghigh heat. This process is alternated with a second weld process, whichis a short-arc, constant voltage welding process. In a still furtherembodiment, the first weld process is a pulse process for high heat. Thesecond weld process is a series of pulses where the energy of the pulsesare determined by a closed loop feedback of the power exerted. A stillfurther example of the invention is an embodiment where the first seriesof pulses in the pulse welding operation are electrode positive to givehigh heat. The second series of pulses is a pulse welding process arenegative, comprising electrode constant voltage pulses. By shiftingbetween these welding processes, the actual welding operation iscontrolled to optimize the performance of the welder.

In accordance with still another aspect of the invention, the first weldprocess of this two stage or two state electric arc welder is a pulsewelding process. This process is continued until the arc voltageindicates a short circuit. Then, the two stage welder is shifted to ashort clearing weld process, such as an STT weld cycle. In the preferredembodiment, the signal to shift from the pulse welding process is notonly dependent upon the indication of a short by a plunge in the arcvoltage, but also on the time of a timer. The arc welder control shiftsfrom the first weld process of the pulse mode into a short clearingprocess only when the short is sustained for a set time. The timer ispreferably set to indicate that the short is maintained for at least 1.0ms and preferably greater than a set time in the range of at least 0.2to 0.5 ms. Consequently, only when there is an actual short, instead ofan incipient short, does the electric arc welder shift into the secondweld process for clearing the detected short circuit.

In accordance with the present invention there is provided an electricarc welder including a high speed switching power supply with acontroller for creating a first and second weld process across the gapbetween a workpiece and a welding wire advancing toward the workpiece.The first process uses a first current waveform and the second processuses a second current waveform. A circuit is used to shift between thefirst and second weld processes, wherein the circuit includes a counterfor counting the waveforms in the first and second processes. The weldershifts from the process being processed to the other weld process whenthe waveform count of the weld process being processed reaches apreselected number for each weld process. By using this two stagewelder, the arc welder can be shifted between two separate and distinctwelding processes in accordance with the count or other parameter.

In accordance with another aspect of the invention, there is a two stagearc welder of the type including a high speed switching power supplywith a controller for creating a pulse wave weld process and a weldprocess to clear a detected short. A circuit is activated to create ashort signal when the arc voltage is below a value indicative of a shortand there is a switch to shift the controller from the pulse waveprocess to the short clearing process by a process shift signal createdupon creation of the short signal. In an aspect of the invention, thetwo stage welder includes a timer to create the shift signal only whenthe short signal is held for a given time which is defined as greaterthan about 1.0 ms and preferably greater than a set time in the generalrange of 0.2 to 0.5 ms. Consequently, when the short is maintained for apreselected time, the two stage welder is shifted from the pulse mode ofoperation to a short clearing mode of operation. In the preferredembodiment, the short clearing mode of operation is an STT weld process.

In accordance with yet a further aspect of the invention, there isprovided a method of operating an electric arc welder of the typeincluding a high speed switching power supply with a controller. Thiscontroller creates a first and second weld process across a gap betweenthe workpiece and the welding wire advancing toward the workpiece by awire feeder. The first process of the method has a first currentwaveform. The second process has a second waveform. The method comprisesshifting between the first and second weld processes and is implementedby counting the waveforms in the first and second processes. The weldprocess being performed is shifted to the other process when thewaveform count of the process being performed reaches a selected number.In a further aspect of the present invention there is a provision of amethod of operating an electric arc welder including a high speed switchand power supply with a controller for creating a pulse wave process anda short clearing weld process. The method comprises creating a shortsignal when the arc voltage is below a value indicative of a short andthen shifting the controller from the pulse wave process to the shortclearing process by a shift signal created upon detection of the shortcircuit. In this method, the shift signal is created only when the shortsignal is held for a given time which in practice is less than 1.0 msand actually in the general range of 0.20-0.50 ms.

The primary object of the present invention is the provision of a twostage electric arc welder that alternately performs two weldingprocesses during a single welding operation.

Yet another object of the present invention is the provision of a twostage arc welder, as defined above, which arc welder has a counter tocount the cycles of one process to determine when there is to be a shiftin the process being performed by the welder.

Still a further object of the present invention is the provision of atwo stage arc welder, as defined above, which two stage arc welderperforms a pulse welding process until a non-incipient short isdetected. Then, the two stage welder is shifted into a second mode ofoperation for clearing the short.

Another object of the present invention is the provision of a method ofoperating a two stage arc welder, as defined above.

Still a further object of the present invention is the operation of atwo stage arc welder, as defined above, which two stages involve one ofmany combinations of a distinct first welding process and a distinct,different second welding process. The two processes alternate back andforth during a single welding operation.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a combined block and wiring diagram illustrating the preferredembodiment of the two stage arc welder of the present invention;

FIG. 2 is a flow chart in block diagram format of a method and operationfor the two stage arc welder, whereby a detected non-incipient shortshifts the welding process being performed;

FIG. 3 is a flow chart in block diagram format showing a furtherimplementation of the two stage welder, constructed in accordance withthe present invention; and,

FIG. 4 is a current graph illustrating the operation of the two stagewelder in accordance with the implementation of the inventionillustrated in FIG. 3.

PREFERRED EMBODIMENTS

Referring now to the drawings, wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, FIG. 1 shows a novel two stage welder Awith a power source 10 comprising a high speed switching power supplyillustrated as inverter 12 having a three phase power supply input 14converted by rectifier 16 into a DC rail in lines 20, 22. Output winding30 of inverter 12 is the primary winding of transformer T having asecondary winding 32 for supplying current to a rectifier network 40.This network provides a current level through positive lead 42 andnegative lead 44. A standard small inductor 50 is connected to astandard contact tip 54, through which passes a welding wire 60 thatforms electrode E spaced from workpiece W to define an arc gap throughwhich the current is passed during the arc welding process. Welder Aperforms many types of electric arc welding by passing a current of apreselected shape across the gap between electrode E and workpiece W. Asthe arc melts wire 60 and workpiece W to perform a welding operation,wire feeder 100 pulls wire from reel 102 at a speed (WFS) determined bythe rotational speed of motor 104. This speed is read by a feedbacktachometer 110 and is controlled by the input voltage to pulse widthmodulator 112 from the output of error amplifier 114. This amplifier hasa first input 120 which is the voltage representing the desired wirefeed speed (WFS). This speed may be controlled by an analog circuit ormore appropriately from a look-up table from wave shaper 180. The inputvoltage 120 determines the speed of motor 104, which actual speed ismonitored by tachometer 110 for comparison with the voltage on line 120.The actual speed feedback is the voltage on input line 122. In thismanner, the wire feed speed is coordinated with the weld process beingimplemented by welder A. The current wave shape across electrode E andworkpiece W is determined by software controller 130 of the typeincluding a software pulse width modulator 132 for generating a voltageon output control line 134 at a pulse rate determined by the setfrequency of oscillator 136. In this manner, the high frequency pulseson line 134 are controlled by the voltage on line 140, which voltage isthe output of a second error amplifier 150 having a first inputcontrolled by current detecting or sensing shunt 152. The voltage online 154 is representative of the arc current of the welding process. Acommand signal on line 160 is compared to the actual arc currentrepresented by the voltage on line 154 to cause the pulse widthmodulator 152 to follow the desired wave shape from wave shaper orgenerator 180 by way of command line 160. The wire feed speed to erroramplifier 114 is also directed from the wave shaper or generator. Thegenerator 180 is of the synergistic type so that both the command signal160 and the wire feed speed signal or voltage (WFS) on line 120 arecoordinated.

In accordance with the novel aspect of welder A, there is provided aswitch 190 which, in practice, is a software switch having a firstposition 192 and a second position 194, as shown in FIG. 1. When inposition 192, wave shaper 180 is controlled in accordance with a firstProcess A from process control system 200 for Process A. In this manner,process control system 200 is connected to the synergistic wave shaper180 to implement Process A from the wave shaper 80 by way of controller130. In a like manner, when switch 190 is in position 194, processcontrol system 202 causes wave shaper 180 to implement the secondProcess B by way of the signal on command line 160. Thus, by shiftingswitch 190 between positions 192, 194, two separate welding processesare performed by welder A. Of course, it is within the present inventionto have switch 190 with more than two positions so that the welder canprocess in sequence or in series more than two welding processes, ifsuch operation is desired. In practice, it is preferred that only twoseparate weld processes be performed alternately by welder A. Inaccordance with another aspect of the invention, the position of switch190 is controlled by logic on dashed line 210 from the output of cyclecounter 212. The counter counts each cycle during either Process A orProcess B. At the end of the count, as set by count selector 214 orcount selector 216, the logic on line 210 shifts switch 190 into theother position for implementing the other weld process. Counter 212counts to a number CA and then shifts to Process B which is maintaineduntil the counter counts to a number CB. Then, switch 190 shifts back tothe first process, i.e. Process A. In the preferred embodiment, one ofthe processes is a high heat process and the other is a low process. Thenumbers CA and CB are essentially the same. Thus, the welding operationinvolves a low heat portion and high heat portion which are repeatedlyimplemented during the total welding process to control the performanceof the welding operation whether it is STT, pulse or otherwise. As willbe shown, various weld processes can be alternately selected by acounter. Indeed, the welder A can be interactive so that the shift fromone process to the other is determined by parameters as distinguishedfrom count numbers. For instance, the voltage sensor 170 produces avoltage on 172 that detects a short, which is used in FIG. 2 fortransition between the first Process A and the second Process B whereinthe second process is an arc clearing process. The counts can bedrastically different and the interactive parameters can be selected toshift into a preselected process after a given process transitions intoa detectable weld condition.

In practice, Process A is normally a high energy process and Process Bis a low energy process. The count numbers CA and CB are essentially thesame. To change the welding operation, number CA is increased or numberCB is decreased to increase the heat during the welding operation. In alike manner, to decrease the heat, the number CA is decreased or thenumber CB is increased. Of course, combinations of these increases ordecreases could be used in selecting the desired total heat during awelding operation. In a preferred embodiment, Process A and Process Bare the same, but with different size waveforms. It may be pulse weldingor STT welding. However, in accordance with the invention, the processescould be completely diverse. For instance, in practice, Process A is aconstant voltage spray process with high heat and Process B is a pulsedGMAW low heat. Counter 212 is set by count selectors 214, 216 to thedesired total heat for the welding operation. In practice, Process A isa pulse welding process with high heat whereas Process B is an STT weldprocess with a lower wire feed speed. Also, in practice Process A is apulse welding process with higher heat and Process B is a short-arcconstant voltage process. A still further implementation of the presentinvention Process A is a pulse welding process and Process B is a closedloop control process, such as a process wherein the current iscontrolled by the output power. Yet a further implementation of thepresent invention is where Process A is a pulse electrode positive andProcess B is an electrode negative constant voltage weld process. Inthat implementation of the present invention, a polarity switch is addedin the output circuit before inductor 50, which polarity circuit isshifted at the same time as switch 190. Other implementations of thepresent invention involve various combinations of welding process toperform the desired overall weld operation.

An interactive control system 220 is schematically illustrated in FIG.2, wherein the wave shaper generator and control 222 creates the voltageon control line 134, as previously described. Control 130 is in block222. The voltage controls power supply 12 which is monitored by aprocess control network 224 together with the voltage on line 172 fromvoltage sensor 170, shown in FIG. 1. Timer 226 of the process controlnetwork is set to a time generally greater than about 1.0 ms andpreferably greater than a set time in the general range of 0.2-0.5 ms.The output from the timer network is a logic on line 232 directed to adecision block 230 to decide whether or not there is a short circuitthat has been detected for a time greater than the time set of time 226.The position of switch 190 is controlled by decision block 230. Whenthere is a short that exceeds the set time of timer 226, switch 190 isshifted into position 194. Thus, when there is a long term non-incipientshort, switch 190 shifts to the alternate position 194 to implement thesecond weld process. In this implementation of the present invention,the first process is a pulse wave form controlled in accordance with thewave shape determined by a system shown as block 240. Block 242represents a system to create an STT wave form or other short clearingweld process. System 220 performs the first mode of operation defined asa pulse wave form controlled by the system represented by block 240.Whenever there is a short, the voltage on line 172 drops down below athreshold. This determines a short circuit. Such detected condition istimed by timer 226. If the time of the short exceeds the set time of thetimer, the logic on line 232 indicates to the decision block that thereis a non-incipient actual short circuit. This logic immediately shiftsthe software switch 190 to the arc clearing weld process, indicated asan STT process. When the short is cleared in accordance with the shortclearing process, the voltage on line 172 immediately shifts to a plasmalevel or arc voltage. This is above the threshold and causes decisionblock 230 to shift switch 190 into position 192 for implementation ofthe pulse wave form controlled by the system represented by block 240.Consequently, system 220 does not involve a cycle counter, but senses awelding parameter for actual shifting of the weld process from one weldprocess to the other. This happens rapidly and occurs whenever theselected parameter is detected.

In FIGS. 3 and 4, system 250 includes a low heat weld processrepresented by block 260. Process A is a low heat STT weld process. In alike manner, a high heat STT weld process is represented by block 262.Counter 212 causes first STT pulses 260 a to be processed as shown inFIG. 4. After the desired number of STT pulses 260 a have been countedby cycle counter 212, switch 190 is shifted into position 194 by thelogic on line 210. This generates the large, or high heat, STT pulses262 a, as shown in FIG. 4. These high heat pulses are counted inaccordance with the selected number for counter 212. In this manner, thenumber of waveforms or cycles of low and high STT is adjusted todetermine the total heat during a welding operation.

The invention involves a two or more stage welder which implements insequence distinctly different welding processes. Preferably, theduration of these processes is determined by a counter; however, aparameter can be used for shifting between the weld processes. Onlyrepresentative processes have been discussed and other weld processescan be used when implementing the invention.

1-54. (canceled)
 55. An electric arc welder including a power sourcebased on a high speed switching inverter for creating a current waveformfor a specific welding process between an electrode and a workpiece,said waveform created by a series of current controlling pulses from apulse width modulator, said pulses having a width determining the realtime current of said waveform, and a switch to change between two weldprocesses upon receipt of a signal to said switch.
 56. An electric arcwelder as defined in claim 55 wherein said switch is operated inresponse to a counter to count cycles.
 57. An electric arc welder asdefined in claim 55 wherein said switch is operated in response to asensed welding parameter.
 58. An electric arc welder as defined in claim55 wherein said switch is operated in response to an arc voltage levelmonitored by a sensor.
 59. An electric arc welder as defined in claim 55wherein said switch is operated in response to a timer.
 60. An electricarc welder including a power source based on a high speed switchinginverter for creating a current waveform for a specific welding processbetween an electrode and a workpiece, said waveform created by awaveform generator having an output controlling a pulse width modulatorin accordance with a selected input circuit to said generator, and aswitch to change said selected input circuit to change between two weldprocesses upon receipt of a signal to said switch.
 61. An electric arcwelder as defined in claim 60 wherein said switch is operated inresponse to a counter to count cycles.
 62. An electric arc welder asdefined in claim 60 wherein said switch is operated in response to asensed welding parameter.
 63. An electric arc welder as defined in claim60 wherein said switch is operated in response to an arc voltage levelmonitored by a sensor.
 64. An electric arc welder as defined in claim 60wherein said switch is operated in response to a timer.
 65. An electricarc welder including a high speed switching power supply with acontroller for creating a pulse wave weld process using a first currentwaveform comprising a first series of pulses and a weld process to cleara short using a second current waveform comprising a second series ofpulses, a circuit activated to create a short signal when the arcvoltage is below a value indicative of a short and a switch to shiftsaid controller from said pulse wave process to said short clearingprocess by a process shift signal created upon creation of said shortsignal.
 66. An electric arc welder as defined in claim 65 including atimer to create said shift signal only when said short signal is heldfor a given time.
 67. An electric arc welder as defined in claim 65wherein said time is generally greater than 1.0 ms.
 68. An electric arcwelder as defined in claim 65 wherein said time is greater than a settime in the general range of 0.2 to 0.5 ms.